I just put together a K8NSC-939 board with an X2 4400+ and 4x 512mb PQI dimms. With all four dimms in, or with slot 1 and 2 populated, I get one long beep, and no post. With slots 1 and 3 populated, it will post, but then I get the message "Memory not optimized", and it says to check the manual...